The present invention relates to a novel fluorine-containing monomeric ester compound of an unsaturated carboxylic acid. More particularly, the invention relates to a novel fluorine-containing ester compound of acrylic or methacrylic acid as a monomeric compound for the preparation of a polymeric resin suitable as a base resin in photoresist compositions.
Along with the trend in recent years in the technology of semiconductor devices toward a higher and higher degree of integration, LSIs having patterning fineness of the design rule 0.20 μm are already under mass production and a schedule for the industrial production of LSIs of a design rule 0.15 μm is now under programming at a high pace.
While the manufacturing process of semiconductor devices almost always involves fine patterning of a resist layer on a substrate such as silicon wafers by the photolithographic technology utilizing a photoresist composition, the major current for the selection of high-performance photoresist compositions is for the use of a positive- or negative-working chemical-amplification photoresist composition, optionally, in combination with an antireflection coating film to intervene between the photoresist layer and the substrate surface. When an improvement in the photoresist composition or photoresist layer is combined with other improvements including the use of an improved photomask such as a halftone mask and Levenson mask and improvement in the light exposure machines such as the annular illumination, exposure by scanning and use of an optical system of a larger numerical aperture, a patterning fineness of a design rule down to about 0.13 μm is expected to be practically accomplished in the near future.
Needless to say, on the other hand, such fineness of the photolithographic patterning can be accomplished only by the use of an exposure light of an extremely small wavelength. In this regard, the promising short-wavelength light sources to be used in the photolithographic technology of the coming ages or next to the coming ages include ultraviolet lights of 200 nm or shorter wavelength exemplified by the vacuum ultraviolet light (VUV) such as the ArF excimer laser beams of 193 nm wavelength, F2 laser beams of 157 nm wavelength and Ar2 laser beams of 126 nm wavelength and the extreme ultraviolet light (EUV) of 13 nm wavelength.
It is essential in the formulation of a photoresist composition suitable for use in the patterning procedure by the use of the above-mentioned exposure light of an extremely small wavelength that, as in the formulation of photoresist compositions for exposure with KrF excimer laser beams, the base resin ingredient, as the key factor to determine the quality such as pattern resolution and dry etching resistance, is selected from those having high transparency to the exposure light and a structure highly resistant against dry etching.
In this regard, proposals are made in the prior art for the base resin of photoresist compositions including fluorine-containing polymers obtained from a fluorine-containing methacrylate ester monomer by introducing three fluorine atoms as a trifluoromethyl group onto the α-carbon atom of an acrylate ester compound (Japanese Patent Kokai 61-190511, 64-43512, 3-261952, 4-42229 and 4-52648) and a homo- or copolymer of α-trifluoromethyl-1-adamantyl acrylate (Japanese Patent Kokai 9-43848).
When a polymeric resin as desired for a radiation-sensitive resist composition is to be prepared by polymerizing such an acrylate eater monomer having a trifluoromethyl group on the α-carbon atom, however, the monomer cannot be polymerized by the mechanism of radical polymerization but can be polymerized only by the anionic polymerization by the use of n-butyllithioum or pyridine as the catalyst with little versatility relative to the selection of the polymerization procedure. In addition, such a resin has a main chain structure consisting of the monomeric units of the acrylate ester and polycyclic hydrocarbon groups in the pendants so that the transparency of the resin to the exposure light of 200 nm or shorter wavelength cannot be high enough.
With an object to solve this problem, the inventors conducted extensive investigations and previously discovered a promising polymeric resin having a monomeric unit structure derived from an ester of a polycyclic unsaturated hydrocarbon compound represented by the general formula in which X is an acid-dissociable solubility-reducing group, Y is an electron-attracting group and m is 0 or 1.
As compared with the polymeric resin, such as an acrylic polymer, having pendant groups to exhibit improved dry etching resistance, the aforementioned polymeric resin having a main chain structure comprising norbornene rings is excellent in the dry etching resistance but is economically disadvantageous due to the high cost for the synthetic preparation of the monomer compound by a complicated method involving the Diels-Alder reaction from cyclopentadiene or dicyclopentadiene.